---
title: "Tools"
---

MCP Tools enable executable operations on the database. DBHub provides SQL execution capabilities with support for transactions and multiple statements.

## Supported Tools

| Tool        | Command Name  | Description                                                         | PostgreSQL | MySQL | MariaDB | SQL Server | SQLite |
| ----------- | ------------- | ------------------------------------------------------------------- | :--------: | :---: | :-----: | :--------: | ------ |
| Execute SQL | `execute_sql` | Execute single or multiple SQL statements (separated by semicolons) |     ✅     |  ✅   |   ✅    |     ✅     | ✅     |

## Execute SQL

Execute SQL queries and statements on your database.

### Features

- **Single statements**: Execute a single SQL query or command
- **Multiple statements**: Separate multiple statements with semicolons (`;`)
- **Transactions**: Wrap operations in `BEGIN`/`COMMIT` blocks for atomic execution
- **Read-only mode**: When enabled with `--readonly` flag, only SELECT and read-only operations are allowed
- **Row limiting**: Configure `--max-rows` to limit SELECT query results

### Single Query

Execute a single SELECT, INSERT, UPDATE, or DELETE statement.

<CodeGroup>
```sql SELECT
SELECT * FROM users WHERE status = 'active' LIMIT 10;
```

```sql INSERT
INSERT INTO users (name, email) VALUES ('Alice', 'alice@example.com');
```

```sql UPDATE
UPDATE users SET last_login = NOW() WHERE id = 123;
```

```sql DELETE
DELETE FROM sessions WHERE expires_at < NOW();
```
</CodeGroup>

### Multiple Statements

Execute multiple SQL statements in sequence by separating them with semicolons.

```sql
INSERT INTO users (name, email) VALUES ('Alice', 'alice@example.com');
INSERT INTO users (name, email) VALUES ('Bob', 'bob@example.com');
INSERT INTO users (name, email) VALUES ('Charlie', 'charlie@example.com');
```

<Note>
Each statement is executed sequentially. If one statement fails, subsequent statements may not be executed depending on the database error handling.
</Note>

### Transactions

Wrap multiple operations in a transaction to ensure atomicity. Use `BEGIN`/`COMMIT` for successful transactions or `ROLLBACK` to undo changes.

<CodeGroup>
```sql Successful Transaction
BEGIN;
UPDATE accounts SET balance = balance - 100 WHERE id = 1;
UPDATE accounts SET balance = balance + 100 WHERE id = 2;
COMMIT;
```

```sql Rollback Transaction
BEGIN;
UPDATE accounts SET balance = balance - 100 WHERE id = 1;
-- Something went wrong, undo changes
ROLLBACK;
```
</CodeGroup>

### DDL Operations

Create, alter, or drop database objects.

<CodeGroup>
```sql CREATE TABLE
CREATE TABLE products (
  id SERIAL PRIMARY KEY,
  name VARCHAR(255) NOT NULL,
  price DECIMAL(10, 2) NOT NULL,
  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);
```

```sql ALTER TABLE
ALTER TABLE products ADD COLUMN category VARCHAR(100);
```

```sql CREATE INDEX
CREATE INDEX idx_products_category ON products(category);
```

```sql DROP TABLE
DROP TABLE IF EXISTS temp_data;
```
</CodeGroup>

<Warning>
DDL operations are not allowed in [read-only mode](/config/server-options#readonly). Use read-only mode when connecting to production databases to prevent accidental schema changes.
</Warning>

## Read-Only Mode

Enable read-only mode to restrict SQL execution to safe, read-only operations:

```bash
npx @bytebase/dbhub --readonly --dsn "postgres://user:pass@localhost:5432/mydb"
```

In read-only mode, only [allowed SQL keywords](https://github.com/bytebase/dbhub/blob/main/src/utils/allowed-keywords.ts) are permitted, including:

- `SELECT` queries
- `SHOW` commands
- `DESCRIBE` commands
- `EXPLAIN` queries
- Other read-only operations

<Tip>
Use read-only mode when connecting to production databases to prevent accidental data modifications or schema changes.
</Tip>

## Row Limiting

Limit the number of rows returned from SELECT queries to prevent accidentally retrieving too much data:

```bash
npx @bytebase/dbhub --max-rows 1000 --dsn "..."
```

- Only applied to SELECT statements, not INSERT/UPDATE/DELETE
- If your query already has a `LIMIT` or `TOP` clause, DBHub uses the smaller value
- Can be configured per-database in [multi-database TOML configuration](/config/multi-database)
